Construction and Development Stormwater Effluent Guidelines

Stormwater runoff from construction sites is one of the largest sources of water pollution in the United States, carrying sediment, nutrients, metals, and other pollutants into streams and waterways. 40 CFR Part 450 establishes technology-based effluent limitations for construction and land development sites — the first national numeric effluent standard applied to construction stormwater, finalized in 2009.

Current Rule (2026)

Legal Authority

• 33 U.S.C. § 1311 — Clean Water Act § 301: requires point source discharges to meet technology-based effluent limitations; authorizes EPA to establish effluent limitation guidelines (ELGs) requiring best practicable technology (BPT), best available technology (BAT), and best conventional technology (BCT)
• 33 U.S.C. § 1316 — Clean Water Act § 306: new source performance standards (NSPS); EPA designates categories of new sources and establishes the most stringent technology-based standards applicable
• 33 U.S.C. § 1342 — NPDES permit program: EPA and authorized states issue permits requiring compliance with ELGs and water quality standards; construction operators must obtain NPDES coverage, typically through a Construction General Permit (CGP)
• 40 CFR Part 450 — EPA implementing regulations establishing the C&D effluent limitation guidelines

Key Mechanics

40 CFR Part 450 applies to construction sites disturbing 1 acre or more (or smaller sites that are part of a larger common plan of development exceeding 1 acre). The rule imposes two types of requirements: (1) BMP requirements — a specific suite of erosion and sediment controls, soil stabilization, dewatering controls, and pollution prevention measures that must be implemented regardless of actual discharge turbidity; and (2) a numeric turbidity limit of 280 NTU in discharge (the BAT/NSPS standard), which applies where turbidity measurement is feasible. Sites comply through NPDES permit coverage (usually a Construction General Permit), which incorporates Part 450 requirements as permit conditions. CWA violations carry civil penalties up to $68,446/day per violation (2026 inflation adjustment).

What This Rule Does

40 CFR Part 450 contains effluent limitation guidelines (ELGs) for the construction and development point source category under the Clean Water Act. ELGs are technology-based standards — they reflect what the best-performing construction sites are achieving through best management practices, regardless of receiving water quality.

The rule's central numeric standard is a turbidity limit of 280 NTU (nephelometric turbidity units) in the discharge, representing the level achievable with best available technology. Additionally, the rule requires that construction operators implement a specific suite of best management practices (BMPs):

• Erosion and sediment controls (silt fences, sediment basins, erosion blankets, check dams)
• Soil stabilization (seeding, mulching, or covering disturbed areas within 14 days of final grading)
• Dewatering controls (settling or filtering water pumped from excavations before discharge)
• Pollution prevention measures (proper storage of fuels, concrete washout, construction materials)
• Surface outlet protection for sediment basins and traps

Key Provisions

• § 450.10 — Applicability: applies to construction activity requiring NPDES permit coverage; the construction general permit (CGP) issued by EPA or authorized states incorporates these ELG requirements; does not apply to activities covered by other stormwater ELGs (e.g., mining, oil and gas construction)
• § 450.11 — General definitions: "new source" means a construction operation commencing after February 1, 2010; "infeasible" means not technologically possible or not economically practicable in light of best industry practices
• § 450.21 — BPT (Best Practicable Technology) standards: requires implementation of erosion and sediment controls, soil stabilization, dewatering controls, pollution prevention, and surface outlet protection; these are the BMP requirements that apply to all covered construction sites
• § 450.22 — BAT (Best Available Technology) standards: adds a numeric turbidity limit of 280 NTU; however, if measurement of turbidity is infeasible at a site (e.g., no accessible sampling point), the operator may comply through BMPs alone; BAT also prohibits discharges that cause or contribute to exceedances of applicable water quality standards
• § 450.23 — BCT standards for conventional pollutants: same as BPT for conventional pollutants (TSS, BOD, pH, fecal coliform, oil and grease)
• § 450.24 — NSPS (New Source Performance Standards): most stringent tier; applies to construction operations that qualify as "new sources"; requires compliance with all BMP requirements and the 280 NTU turbidity limit from day one of operation, with no variance available for the 10-year NSPS period

How It Affects You

Construction operators (developers, contractors, homebuilders) disturbing 1 acre or more must obtain NPDES permit coverage (usually through coverage under a Construction General Permit) and comply with Part 450 requirements. This means installing and maintaining erosion and sediment controls throughout the project, stabilizing disturbed soil promptly, and ensuring that discharge turbidity doesn't exceed 280 NTU where it can be measured.

Permit inspectors and state regulators — the ELG standard is incorporated into Construction General Permit conditions; violations of the 280 NTU turbidity standard or the BMP requirements are enforceable CWA violations subject to substantial daily civil penalties (judicially-imposed CWA § 309(d) civil penalty cap is $68,446/day per violation as of the 2026 inflation adjustment).

Homebuilders building single lots that are part of a larger common plan of development exceeding 1 acre are covered even if the individual lot disturbance is less than 1 acre.

Statutory Authority

This rule implements:

• 33 U.S.C. § 1311 — CWA § 301: effluent limitations shall require application of best practicable technology by July 1, 1977, best available technology by 1989 (or later dates); new source performance standards apply to new sources in designated categories

Recent Rulemakings

• 74 FR 63057 (Dec. 1, 2009) — final Construction and Development ELG rule; effective February 1, 2010; established 280 NTU numeric turbidity limit and BMP requirements; the numeric limit faced legal challenge but was upheld
• 80 FR 25236 (May 4, 2015) — clarification of BMP requirements

Pending Action

No pending rulemaking to amend 40 CFR Part 450 as of 2026. EPA's current Construction General Permit (CGP), most recently updated in 2022, incorporates Part 450 requirements. Monitor EPA's NPDES permits program page for any future CGP revisions that could change on-the-ground compliance obligations.